Composition of the earth

Dr. Ahmad Redaa

2024-09-02

Key Topics

Composition of the Earth

The four components of the earth, Source: Jain, S. (2014)

Interrelationship of Earth components

The four components of the earth, Source: (a) https://byjus.com (b) Jain, S. (2014)

Atmosphere

Definition

Composition of the Atmosphere

Layers of the Atmosphere

  • Troposphere:
    • Closest to Earth, extends up to ~12 km.
    • Weather occurs here.
    • Temperature decreases with altitude.
  • Stratosphere:
    • Extends from ~12 km to 50 km.
    • Contains the ozone layer, which absorbs UV radiation.
    • Temperature increases with altitude due to ozone absorption.
  • Mesosphere:
    • Extends from ~50 km to 85 km.
    • Meteors burn up in this layer.
    • Temperature decreases with altitude.
  • Thermosphere:
    • Extends from ~85 km to 600 km.
    • Temperature increases significantly.
    • Contains the ionosphere, where auroras occur.
  • Exosphere:
    • Outermost layer, extends beyond 600 km.
    • Gradual transition into space.
    • Very low density of particles.

Layers of the Atmosphere, Source: https://byjus.com

Lithosphere

  • Definition: The lithosphere is the land part of the Earth (litho = stone) and includes all the solid materials constituting the Earth, from surface downward.

  • Structure:

    • Composed of both the crust and upper mantle.
    • Extends 80–100 km below the surface.
    • Thickest under continents (~120 km) and thinnest under mid-ocean ridges.
  • Parts of the Plates:

    • Continental Lithosphere:
      • Thicker and less dense.
      • Composed primarily of granite.
    • Oceanic Lithosphere:
      • Thinner and more dense.
      • Composed primarily of basalt.
  • Temperature:

    • Near the mantle surface: ~1,000°C.
    • Temperature increases by 25°C per 1,000 m as you move downward.
    • Reaches up to 3,700°C at the core-mantle boundary.
  • Plate Tectonics:

    • The lithosphere is fragmented into massive plates.
    • These plates fit around the globe like pieces of a jigsaw puzzle.
    • Plates move independently and slide on the asthenosphere.
    • Movement causes earthquakes.

a- Tectonic. b- Chemical (Compositional) and Mechanical layers of the earth and their major characteristics., Source: https://byjus.com

Hydrosphere

  • Definition:
    The hydrosphere encompasses all of Earth’s water, including water in liquid, solid, and vapor forms. It covers every part of the planet, from oceans and rivers to underground aquifers and atmospheric moisture.

  • Coverage Percentage:

    • Total Earth Surface Covered by Water: ~71%
      • Oceans: 97% of Earth’s water, covering about 70% of the surface.
      • Freshwater: 3% of Earth’s water, found in glaciers, ice caps, rivers, lakes, and groundwater.
  • Water Cycle:
    The water cycle describes the continuous movement of water on, above, and below the surface of the Earth. Key processes include:

    • Evaporation: Water from oceans, lakes, and rivers turns into vapor and rises into the atmosphere.
    • Condensation: Water vapor cools and forms clouds.
    • Precipitation: Water falls back to the Earth’s surface as rain, snow, sleet, or hail.
    • Infiltration: Water soaks into the ground, replenishing aquifers.
    • Runoff: Water flows over the land into bodies of water, completing the cycle.
  • Significance:

    • Climate Regulation: Distributes heat around the globe, influencing weather and climate patterns.
    • Supporting Life: Essential for all living organisms, providing hydration and habitats.
    • Geological Processes: Shapes landscapes through erosion and sediment transport.

The Water Cycle, Source: https://www.twinkl.com.tr

Biosphere

Earth’s Interior Structure

The Earth’s interior, Source: Jain, S. (2014)

Earth’s Interior Structure

Understanding Earth Through Seismology

_ Body waves: they are transmitted through Earth materials. - P Waves (Primary Waves): - Definition: P waves are seismic waves that are the fastest and first to be detected. - What ‘P’ Stands For: Primary - Physical Properties: - Compressional waves that move in a push-pull motion. - Travel through solids, liquids, and gases. - Speed: ~6-14 km/s in the Earth’s crust. - Indications: - P waves can pass through the entire Earth, indicating that the outer core is liquid since they slow down and refract.

A compression wave can be illustrated by a spring (like a Slinky) that is given a sharp push at one end. A shear wave can be illustrated by a rope that is given a quick flick., Source: Steven, E. (2015)

Velocity of waves

P wave (red) and S wave (blue) velocity variations with depth in Earth, Source: Steven, E. (2015)

Seismic Discontinuities

The Temperature of Earth’s Interior

Right: generalized rate of temperature increase with depth within Earth.Left: Rate of temperature increase with depth in Earth’s upper 500 kilometres Source: Steven, E. (2015)

The Temperature of Earth’s Interior (2)

Isostasy

Source: Steven, E. (2015)